Document numbering settings define how orders and Accounts Receivable (AR) documents are assigned with unique numbers. Individual document numbering rule can be configured for each document type. For example, sales orders can have "SO00001" as the starting number, renewal orders: "RN00001", and so on.
Document and order numbering of any type is defined by its enumerator class containing a numbering rule.
For clear Billing installation the default starting numbers (enumerator classes) are created. For some types of documents, default starting numbers include letters, some documents have zero default starting numbers. If you want to use own document numbering, adjust starting numbers.
Important: An enumerator class may run out of free digits. As Billing cannot create two orders of one type with the same number under the same vendor, this lead to stop of order processing. Configure the enumerator class according to this article.